Alan Dougan
Fugro GEOS
Donogh Lang
MCS Kenny
Serious incidents associated with deepwater drilling operations and challenging environmental conditions such as high currents highlight the significant risk of unplanned incidents involving the marine riser. Addressing these challenges, Fugro has teamed with MCS Kenny to offer a suite of onboard riser management tools.
Optima allows operators and contractors to plan and monitor operations involving risers, whether deployed for drilling, completion, workover, or light well-intervention.
The benefits of riser management to operators can be cost savings and enhanced safety and engineering integrity of subsea equipment. For example, in 2004 GlobalSantaFe, now part of Transocean, showed that by running simulations with the onboard software, downtime on a well in a high current zone was significantly reduced, saving $2.8 million in rig time alone on a single well.
The software is designed as a simple installation on modern deepwater drilling vessels where parameters such as position, riser angle, and riser tension already are measured. If these parameters are not measured routinely (for example, on earlier generation drilling vessels), Fugro/MCS Kenny can engineer supplementary solutions. The Optima PC can be linked into the vessel’s computer network and configured to share information with other vessel systems.
Riser design and management
In conventional drilling, the riser configuration typically is designed onshore and the configuration passed to the vessel for implementation. The well specific operating criteria (WSOC) are generated and used to manage the drilling operations. The software carries out to the rig the same finite element analysis (FEA) model used to generate the WSOC.
This provides a link between well operations planning and offshore operations. Offshore, the software uses the riser model plus measured vessel, environmental, and riser response data to predict how the riser will respond.
As design is an inherently conservative process, this real-life comparison allows the driller to identify how the riser actually behaves. The driller then can take advantage of the built-in conservatism where it is safe to do so. On occasions where, for example, the environmental conditions are severe, it may be possible to maintain safe operation in more severe conditions than those specified in the WSOC, as demonstrated by GlobalSantaFe.
Optima integrates with the MCS Kenny DeepRiser software, which analyzes drilling risers for all major deepwater drilling contractors. DeepRiser is used by a well riser configuration process while, Optima links the riser model into the offshore environment.
Fugro’s experience in design, installation, and operation of onboard data collection systems provides the mechanism to deliver the integrated package. This approach can:
- Increase the operating window to reduce downtime and save cost
- Increase confidence in riser operations in prevailing or forecast metocean conditions to reduce unplanned incidents
- Reduce annual riser inspection costs by tracking riser joint use and by optimizing inspection programs
- Properly plan dual activity operations onboard for greater efficiency
- Reduce risk of failure by improved system monitoring and operation – staying within operational capacity of riser
- Reduce fatigue and wear on critical riser components, and, perhaps most importantly
- Protect the well.
Optimization during drilling
Optima is used by the drillers. It does not require a dedicated operator. It takes either output from existing vessel systems or manual input to predict the behavior of the riser in the prevailing or forecast metocean conditions. The system provides real-time guidance to optimize drilling and intervention. An operator interface displays key results.
The software is suitable for mobile offshore drilling units, production facilities with drilling capability, and well intervention vessels. The system can be configured to acquire data from a range of vessel systems, including:
- Vessel position and heading
- Tensioner tension and stroke
- Current profile
- Sea state data (significant wave height)
- Riser internal pressure
- Hook load.
Key data are displayed in real-time and alarm limits can be set by the operator to draw attention to exceptional conditions. The operator display includes:
- Operating envelope (based on flex joint angles or other limiting parameters) with vessel and wellhead position
- Optimum vessel position advice for drilling, non-drilling (standby), and completion/workover operations
- Minimum and maximum top tension limits
- Optimum top tension
- Recommended tensioner/hook load split for completion/workover risers.
The Optima computer is stand-alone. It is independent of the vessel, or (other than collecting inputs from vessel systems). Feedback is through the software’s operator display and warning functions.
Main window for online operation.
The system is:
- Designed to allow continuous, safe, and reliable operation
- Based on proven hardware and software modules
- Robust for harsh environments and rough handling
- Designed to meet the general requirements for offshore electrical safety and, where required, operation in hazardous areas.
Continuous monitoring
Optima is to the riser what the DP system is to the vessel. It monitors the prevailing conditions and allows the user to simulate what will happen to the riser in forecast conditions. The software provides advice to reposition the vessel and adjust the riser tension to minimize riser loads and to optimize the operational envelope based on riser response.
The system will monitor and record load changes from unplanned incidents such as vessel drift-off or failure in heave-compensation. All monitored data is stored and can be downloaded for analysis as required.
The FEA model of the riser is used to compute the response of the entire riser system based on real-time measured riser response data (such as riser inclination or strain measurements) and the information obtained from the vessel drilling, position, and environmental systems.
Specifically, the software determines a physically realistic combination of loads that give rise to the measured riser response. This process is flexible and can be configured to use available riser response measurements.
The software has modules for different applications. In its basic form, system software operates in “offline.” In this mode, all relevant data (such as metocean conditions, riser tension, etc.) is entered by the operator and the simulation software generates results that provide guidance for riser operations. In “offline” mode, there is no requirement for interfaces to other vessel systems and the software can simply be installed on a laptop PC on the vessel.
The system has been deployed successfully in this configuration on a number of deepwater drilling rigs, including six Transocean vessels, including the Development Driller II and III, used to control BP’s Macondo blow-out in the Gulf of Mexico.
Offline operation can be augmented with data acquisition capabilities and interfaces to existing vessel systems, allowing the system to acquire data and to operate “online,” or real-time mode.
This may be further augmented by riser instrumentation such as inclinometers (to measure flex joint angles or riser inclination), strain sensors (for fatigue-sensitive applications), and motion measurement units for applications such as vortex-induced vibration detection and measurement.
Real-time guidance
In online mode, the riser management system provides real-time returns, such as the vessel operating envelope, optimum vessel position advice, and the watch circles for the drift-off (DP power-loss) scenario. These are calculated using the prevailing metocean conditions and the measured riser response.
Offline, the system can determine what will happen if the metocean conditions change. For example, the driller can determine what the effect on the operating envelope or the watch circles for the drift-off scenario will be if the sea state or ocean current should change. Typically, these “what if” scenarios use forecast metocean data as input.
Optima provides facilities for simulating a range of riser operations, including:
- Operations: Calculation of operating envelope, optimum vessel position, and optimum riser tension
- Drift-off: Calculation of the watch circles for the DP power-loss scenario
- Deployment/retrieval: Determine the feasibility of deploying/retrieving the riser in prevailing or forecast conditions
- Hang off: Determine the feasibility of performing a hard or soft hang off of the riser
- Riser disconnect: Calculate the excursion of the riser base after disconnect and compute the optimum vessel position for a successful disconnect
- SIMOP: Plan operations to be carried out while drilling
- Drift running: Planning a drift running track
- Transiting: Well-to-well moves.
In addition to the online and offline modes, the system can track and record the usage history of the riser. This allows various parameters to be recorded individually for each riser joint, including hours of use and fatigue damage sustained. The latter parameter is calculated using the riser model and the measured riser response.
A major benefit for applications with intervention risers is the program’s ability to track fatigue damage accumulated by the riser. Intervention risers can be subject to significant fatigue damage, especially in harsh environment applications. In Norway, operators use the information to optimize riser inspection, eliminate unnecessary inspection costs, and to ensure the ongoing integrity of the intervention riser system.
Typically, one or more subsea strain sensor packages are installed on a riser used for intervention applications to get an accurate measure of the riser response and the fatigue damage sustained. Optima integrates these instrumentation packages.
The system passively interfaces with the WOCS, riser tensioning system, and position monitoring system to read additional inputs such as riser internal pressure, riser tension data, heave compensator stroke, and vessel position data.
Offshore installation and retrieval of riser instrumentation can be done in parallel with other activities to reduce rig time. The riser instrumentation is robust and designed to avoid snagging in the rotary/spider or elsewhere.
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